1. Field of the Invention
The present invention relates to a high pressure fuel supply pump which is used in an internal combustion engine ("internal combustion engine" is hereinafter referred to simply as "engine").
2. Description of the Related Art
A fuel supply system for an engine that uses a conventional high pressure fuel supply pump is illustrated in FIG. 22. Within a fuel tank 201 there is accommodated a fuel pump 202 by which fuel is pressurized to several hundred KPa and forcibly supplied to an intake port 204 of a fuel filter 203. A discharge port 205 of the fuel filter 203 is connected to an intake port 207 of a high pressure fuel supply pump 206. The drive force produced by the reciprocating movement of a piston 211 is transmitted to a camshaft 210 by a connection mechanism composed of a connecting rod 212, a crank shaft 213, and a belt 214, thereby rotating the camshaft 210 of the high pressure fuel supply pump 206. As shown in FIGS. 20 and 21, a pump-driving cam 224 accommodated within a housing 223 of the high pressure fuel supply pump 206 and adapted to rotate integrally with the camshaft 210 causes the reciprocating movement of a plunger 225 of the supply pump 206. The fuel taken in from the intake port 207 is pressurized by the high pressure fuel supply pump 206 to a high pressure level of several MPa to several tens of MPa and is then discharged through a delivery valve 226 to a common rail 209 via a discharge port 208. The high pressure fuel that has accumulated in the common rail 209 is supplied through a branch passage 215 to an injector 217 provided for each air cylinder. Then, the high pressure fuel is injected from the injector 217 directly to a combustion chamber 216 within the air cylinder.
The unnecessary low pressure fuel that is outputted from a bypass discharge port 218 of the high pressure fuel supply pump 206 is returned to the fuel tank 201 through a return passageway 219. A pressure sensor 220 for sensing the pressure of the fuel inside the common rail 209 is disposed thereon, whereby a pressure signal obtained as a result of the detection performed by the pressure sensor 220 is inputted to an electronic control unit 221. The electronic control unit 221 controls the energizing timing of a solenoid valve 222 so that the fuel injection pressure is of optimum level, in correspondence with the pressure signal sensed by the pressure sensor 220 and the operating conditions of the engine such as, for example, the number of engine revolutions, the engine load, and the like, thereby controlling the amount of fuel discharged into the common rail 209. Further, the electronic control unit 221 outputs a control signal to the injector 217 in order to control the fuel injection timing and injection period in accordance with the operating conditions of the engine such as, for example, the number of engine revolutions, the engine load, etc.
However, since in the case of the above-mentioned conventional high pressure fuel supply pump 206, the camshaft 210 and the pump-driving pump cam 224 are built into the housing 223, the high pressure fuel supply pump 206 increases in size and weight due to the existence of the pump cam 224, part of the housing 223 covering this cam 224, and members such as, for example, the bearing of the pump cam 224, oil seal, etc., not shown. Further, since not only does the number of parts employed increase but the housing 223, camshaft 210, and parts associated therewith must necessarily be fabricated with high precision, the problem exists that there is an increase not only in the number of manufacturing steps but the manufacturing cost as well. Furthermore, on the engine side, it is necessary to provide a pump-fixing flange and a pump-fixing stay, thereby giving rise to the problem that the number of fabrication steps increases.
In order to solve the above-mentioned problems, a camshaftless pump for diesel engines is adapted for use in agricultural machinery. However, although this camshaftless pump for diesel engines is small, since the fuel injection timing and fuel amount are controlled by mechanical control based on the use of a fuel reed formed with respect to the plunger, the controllable range thereof is limited. Further, in the case of a multi-cylinder pump, since the same control is simultaneously mechanically performed with respect to all air cylinders by a built-in control rack, the problems exist that (1) separate control cannot be performed with respect to each air cylinder and that (2) the degree of freedom with which the loading space may be utilized is small because it is necessary to load the pump in one place.